"We believe that the fire originated on the middle landing of the stairway leading to the apartment where the victims perished," said Deputy Chief Brant Thompson with the State Fire Marshal's Office.

Investigators have not named any suspects.

The fire destroyed four units in the six-plex located in the 2300 block of Harvard Avenue in Metairie and damaged two others in the same building.

The victims are a woman in her early 40s, a man in his early 30s and another man in his late 50s, said Col. John Fortunato, spokesman for the Jefferson Parish Sheriff's Office. Authorities have not released their names, saying they are awaiting confirmation of their identities.

A fourth resident, a 44-year-old man and the registered tenant of the unit, escaped the fire by jumping from window in the second-floor apartment. He suffered a leg injury in the 15-foot drop, said Fire Prevention Chief Dennis Guidry with the East Bank Consolidated Fire Department.

The surviving resident told investigators he woke just before 3 a.m. as the others told him there was smoke and fire at the apartment's door, according to Fortunato.

Authorities learned later that someone set a fire on the landing of the wooden staircase that was the apartment's only exit, blocking the residents' escape.

"They retreated to a back bedroom," Thompson said. "According to the survivor, they were all gathered in that area, and it was his assumption that they would all jump. But they did not."

Investigators suspect an accelerant was used to start the fire but are awaiting the results of laboratory testing for confirmation, Thompson said.

Detectives from the Sheriff's Office joined arson investigators from the State Fire Marshal's Office and the East Bank Consolidated Fire Department on case.

"Because there are fatalities, we are treating it as a crime scene," Guidry said.